linux-kernel - Re: [PATCH 14/14] uaccess: drop set

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Message-ID: <YgsYD2nW9GjWJtn5@zeniv-ca.linux.org.uk>
Date:   Tue, 15 Feb 2022 03:03:43 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-api@...r.kernel.org, arnd@...db.de,
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Subject: Re: [PATCH 14/14] uaccess: drop set_fs leftovers

On Mon, Feb 14, 2022 at 05:34:52PM +0100, Arnd Bergmann wrote:
> diff --git a/arch/parisc/include/asm/futex.h b/arch/parisc/include/asm/futex.h
> index b5835325d44b..2f4a1b1ef387 100644
> --- a/arch/parisc/include/asm/futex.h
> +++ b/arch/parisc/include/asm/futex.h
> @@ -99,7 +99,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
>  	/* futex.c wants to do a cmpxchg_inatomic on kernel NULL, which is
>  	 * our gateway page, and causes no end of trouble...
>  	 */
> -	if (uaccess_kernel() && !uaddr)
> +	if (!uaddr)
>  		return -EFAULT;

	Huh?  uaccess_kernel() is removed since it becomes always false now,
so this looks odd.

	AFAICS, the comment above that check refers to futex_detect_cmpxchg()
-> cmpxchg_futex_value_locked() -> futex_atomic_cmpxchg_inatomic() call chain.
Which had been gone since commit 3297481d688a (futex: Remove futex_cmpxchg
detection).  The comment *and* the check should've been killed off back
then.
	Let's make sure to get both now...